[3] The species is endemic to highlands in the Albertine Rift in central Africa.

[4] The three long annulated horns in the male T. johnstoni makes it superficially similar to T. jacksonii and T. werneri, and to an extent also to the short-horned T. fuelleborni and the smooth-horned T. oweni,[4] but they are not close relatives.

[5] The specific name johnstoni was given in honour of the British explorer Harry Johnston.

[6][7] T. johnstoni is found in forests at altitudes between 1,000 and 2,500 m (3,300–8,200 ft) in the Albertine Rift of eastern Democratic Republic of the Congo, western Burundi, western Rwanda, and southwestern Uganda, but also tolerates semi-urbanized environments as long as some trees and bushes remain.

[4] T. johnstoni is oviparous, with the female laying 4–23 eggs per clutch.